This invention relates to a tracking radar system which reduces the errors experienced at short range or with relatively large targets caused by the form of tracking noise called angle noise, angle scintillations, angle fluctuations or target glint.
In radar tracking of a target several measurement errors are encountered from characteristics of the target itself. Angular scintillation, glint, is the wandering of the center of reflection of a target from its effective center. This appears on a radar display as an apparent displacement of the target from its mean position. The displacement may consistently vary as is well known in the art. For targets several wavelengths long, such as aircraft, the apparent radar mean position, center, will wander as the target rotates relative to the line-of-sight. When a target is in a radar short-range region, glint becomes a dominant problem for targets extending over several wavelengths. Radar echos received from a single target can be from several points on the target, indicating a rotating group of isolated points and disclosing an apparent multiple-point target. The reflecting points of a multiple-point target are fixed with respect to the target mean position but appear to wander relative to the radar line-of-sight. When uncompensated for, glint can cause a moving target to appear outside of the physical boundary, or extent, of the target.
Angle fluctuations on glint is discussed briefly in the textbook by M. I. Skolnik, Introduction to Radar Systems, McGraw-Hill, New York (1962) at page 186; and in more detail in M. I. Skolnik, Radar Handbook, McGraw-Hill, New York (1970), Chapter 28, pages 28-8 through 28-15.
A glint simulator is covered by Cash et al Pat. No. 3,760,418. A multiple target tracking system with crossed antenna element arrays is disclosed in Vogel Pat. No. 3,323,127. Coleman Pat. No. 3,803,618 discloses a multimode retrodirective array in a conical configuration as shown at 46 in FIG. 4. Rearwin Pat. No. 2,983,920 shows a planar array of microwave antennas, and Kossiakoff et al Pat. No. 3,946,382 is of interest as disclosing an adaptive video processor for distinguishing from many types of noise-like clutter return. None of these references show or suggest reducing the effect of glint in a guidance system.
An optical tracking system using a laser, with a quadrant detector in the tracking receiver, is disclosed in a paper by C. R. Cooke and J. P. Speck, "Precision Aircraft Tracking System" in Proceedings--Optical Tracking Systems, a seminar sponsored by the SPIE Society of Photographic and Instrumentation Engineers, White Sands Chapter, Jan. 18-19, 1971. Durig Pat. No. 4,231,533 covers a laser target tracking system which includes a holographic quadrant selector.